Failure detection device for hydraulic motor and hydraulic drive vehicle

ABSTRACT

A failure detection device for a hydraulic motor according to the present comprises a hydraulic pump ( 3 ) that is driven by a prime mover ( 2 ); a hydraulic motor ( 1 ) that is driven by hydraulic oil discharged from the hydraulic pump ( 3 ); an abnormality detection device ( 35 ) that detects a sign of abnormal operation of the hydraulic motor ( 1 ); and a warning device ( 39, 40 ) that issues a warning when the sign of the abnormal operation of the hydraulic motor ( 1 ) is detected by the abnormality detection device ( 35 ).

This application is a 371 of PCT/JP01/00368 Jan. 19, 2001.

TECHNICAL FIELD

This invention relates to a device that detects a failure of thehydraulic motor installed in the hydraulic drive vehicle such as awheeled hydraulic excavator.

BACKGROUND ART

Generally, the hydraulic drive vehicle such as a wheeled hydraulicexcavator comprises a hydraulic pump, and a hydraulic motor fortravelling which is driven by oil discharged from the hydraulic pump.The output shaft of this hydraulic motor is connected with the inputshaft of the transmission, and the rotation of the hydraulic motor istransmitted to the wheels through the transmission. A drain chamber isprovided to the hydraulic motor, and the drain oil from the hydraulicmotor returns to a reservoir via the drain chamber.

In such a hydraulic drive vehicle as described above, if the hydrauliccomponents or an oil cooler, for example, get damaged, which causes thetemperature of pressure oil to be supplied to the hydraulic motor tobecome high, the viscosity of the pressure oil lowers and the hydraulicmotor may be prevented from its proper operation. In this case, there isa possibility that the hydraulic motor may get damaged. If the hydraulicmotor is damaged, the discharged oil from the hydraulic pump flows intothe drain chamber, and in some cases, it flows into the transmission. Asa result, the transmission is filled with the oil therein, and a greatresistance comes to act on the transmission so that the travellingperformance of the vehicle deteriorates. Moreover, when transmission oilbecomes mixed with the oil from the hydraulic motor, the property of thetransmission oil may be deteriorated, and this may exert a negativeinfluence upon the operation of the transmission.

DISCLOSURE OF THE INVENTION

The present invention is to provide a failure detection device for ahydraulic motor that detects an abnormal operation of the hydraulicmotor at early stages to suppress damage of the hydraulic motor andnegative consequences from this damage to the minimum.

Moreover, the present invention is to provide a hydraulic drive vehiclewhich is equipped with such a failure detection device for a hydraulicmotor.

In order to achieve the above described object a failure detectiondevice for a hydraulic motor according to the present inventioncomprises a hydraulic pump that is driven by a prime mover; a hydraulicmotor that is driven by hydraulic oil discharged from the hydraulicpump; an abnormality detection device that detects a sign of abnormaloperation of the hydraulic motor; and a warning device that issues awarning when the sign of the abnormal operation of the hydraulic motoris detected by the abnormality detection device.

Furthermore, a hydraulic drive vehicle according to the presentinvention comprises a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; an abnormality detection device that detects asign of abnormal operation of the hydraulic motor for traveling; and awarning device that issues a warning when the sign of the abnormaloperation of the hydraulic motor for traveling is detected by theabnormality detection device.

Therefore, it is possible for an operator to recognize an abnormal stateof the hydraulic motor at an early stage so that damage upon thehydraulic motor and negative effects attributable to the damage can meminimized.

It is also acceptable to restrict a driving of the hydraulic motorinstead of issuing a warning. The hydraulic motor may be a hydraulicmotor for traveling, and it is desirable to lower the rotational speedof the prime mover when the sign of the abnormal operation of thehydraulic motor for traveling is detected. It is also acceptable toprevent the vehicle from traveling and to apply a brake when the vehiclehas stopped. Furthermore, it is desirable to prevent a restarting of theprime mover when the sign of the abnormal operation of the hydraulicmotor for traveling is detected. In addition, a warning may be issued aswell.

The sign of the abnormal operation of the hydraulic motor can bedetected based upon a temperature of drain oil from the hydraulic motor,a rotational speed of the hydraulic motor, or an inlet pressure of thehydraulic motor.

It is possible to disable the warning device from issuing the warning orto disable a drive restriction on the vehicle when the working state isdetected.

It is desirable to reset the above-described control in response to areset command. The reset command may be issued upon stopping of theprime mover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the first embodiment of the presentinvention.

FIG. 2 is sectional view of a traveling motor to which the presentinvention has been applied.

FIG. 3 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the firstembodiment of the present invention.

FIG. 4 is a flow chart showing an example of procedure executed by thecontroller.

FIG. 5 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for thehydraulic motor according to the second embodiment of the presentinvention.

FIG. 6 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the secondembodiment of the present invention.

FIG. 7 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the third embodiment of the presentinvention.

FIG. 8 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the thirdembodiment of the present invention.

FIG. 9 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fourth embodiment of the presentinvention.

FIG. 10 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the fourthembodiment of the present invention.

FIG. 11 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fifth embodiment of the presentinvention.

FIG. 12 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the fifthembodiment of the present invention.

FIG. 13 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the sixth embodiment of the presentinvention.

FIG. 14 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the sixthembodiment of the present invention.

FIG. 15 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the seventh embodiment of the presentinvention.

FIG. 16 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the seventhembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A wheeled hydraulic excavator that is equipped with a failure detectiondevice according to the first embodiment of the present invention willnow be described with reference to FIGS. 1 through 4. The wheeledhydraulic excavator comprises a wheeled undercarriage upon which anupper-structure is rotatably mounted, and a working attachment is fittedto this upper-structure. A hydraulic motor 1 for traveling which isdriven by a hydraulic circuit for traveling shown in the FIG. 1 isprovided in the undercarriage.

As shown in FIG. 1, hydraulic oil is discharged from a main pump 3 whichis driven by an engine, the direction and flow rate of the dischargedoil are controlled by a control valve 4, and then the hydraulic oil issupplied to a traveling motor 1 via a brake valve 6 with a built-incounterbalance valve 5. A transmission 7 is connected with an outputshaft 1 a of the traveling motor 1. The rotational speed of thetraveling motor 1 is changed by the transmission 7, and is transmittedto tires 10 through propeller shafts 8 and axles 9. Thus, the wheeledhydraulic excavator is propelled. At this time, the leakage oil from thetraveling motor 1 is collected to a reservoir through a drain line(drain chamber) 11. It should be noted that the pressure oil from themain pump 3 is also supplied to a hydraulic circuit for working which isnot shown in the figure, and drives actuators for working. The directionof changeover and operation amount of the control valve 4 are controlledby pilot pressure from a pilot control circuit. The traveling speed ofthe vehicle can be controlled by controlling the amount by which thecontrol valve 4 is operated. The pilot control circuit comprises a pilotpump 21, a traveling pilot valve 23 that generates a secondary pilotpressure P1 according to the amount by which an accelerator pedal 22 isstepped upon, a slow-return valve 24 that delays oil returning to thepilot valve 23, and a forward/reverse switchover valve 25 which is usedfor selecting forward traveling, reverse traveling or neutral for thevehicle. The forward/reverse switchover valve 25 is constituted of asolenoid-controlled directional control valve, and its position ischanged over by operating a switch not shown in the figures.

FIG. 1 shows the situation with the forward/reverse switchover valve 25in its neutral (N) position, and moreover when the traveling pilot valve23 is not being operated. Accordingly, the control valve 4 is in itsneutral position, the pressure oil from the main pump 3 returns to thereservoir, and the vehicle remains stopped. When the forward/reverseswitchover valve 25 is switched to its forward traveling position (Fposition) or to its reverse traveling position (R position) by theoperation of the switch, and then the accelerator pedal 22 is steppedupon, the secondary pressure P1 according to the amount by which theaccelerator pedal is operated acts on a pilot port of the control valve4. The control valve 4 is operated by the operation amount correspondingto the secondary pilot pressure P1. Thus, the discharged oil from themain pump 3 is led to the traveling motor 1 via the control valve 4, acenter joint 12 and the brake valve 6, so as to drive the travelingmotor 1. At this time, the leakage oil from the traveling motor 1 iscollected to the reservoir through a drain line (drain chamber) 11.

When the accelerator pedal 22 is released during vehicle traveling, thepressure oil from the pilot pump 21 is interrupted by the travelingpilot valve 23, and an outlet port of the traveling valve is connectedto the reservoir. As a result, the pressure oil having acted on thepilot port of control valve 4 returns to the reservoir via theforward/backward switchover valve 25, the slow return valve 24 and thetraveling pilot valve 23. At this time, the returning oil flow isrestricted by the restriction of the slow return valve 24, so that thecontrol valve 4 returns to its neutral position gradually. When thecontrol valve 4 returns to its neutral position, the supply of thepressure oil (drive pressure) is interrupted, and the counterbalancevalve 5 is then switched to its neutral position as shown in FIG. 1.

At this time, the vehicle continues to progress due to its inertiaforce, and the operation of the traveling motor 1 changes over frommotor action to pump action, in which its B port is its suction (inlet)port and its A port is its discharge (outlet) port in FIG. 1. Flow ofthe pressure oil from the traveling motor 1 is restricted by therestriction of the counterbalance valve 5 (neutral restriction), thepressure between the counterbalance valve 5 and the traveling motor 1then rises and acts on the traveling motor 1 as brake pressure. As aresult, the traveling motor 1 generates the brake torque to slow thevehicle down. If, during the pump operation, the quantity of oil flowinginto the traveling motor 1 becomes insufficient, the additional oil issupplied from a make-up port 13 thereto. The maximum brake pressure isregulated by relief valves 14 and 15.

A governor 2 a of the engine 2 is connected with a pulse motor 32 via alink mechanism 31, and the rotational speed of engine 2 is controlled byrotation of the pulse motor 32. In particular, the engine speed isincreased by the normal rotation of the pulse motor 32, while it isdecreased by the reverse rotation of the pulse motor. A potentiometer 33is connected with the governor 2 a via the link mechanism 31, and thispotentiometer 33 detects a governor lever angle corresponding to therotational speed of the engine 2. The detected value is input to thecontroller 30 as a control rotational speed Nθ.

Furthermore, the controller 30 is connected with a pressure sensor 34that detects the secondary pilot pressure P1 generated by the travelingpilot valve 23, corresponding to the pedal operation amount, atemperature sensor 35 that detects temperature of drain oil from thetraveling motor 1, a reset switch 36, and a key switch 37 that is turnedon/off according to the operation of an engine key, respectively. Apower source 38 is connected with the key switch 37, and the electricalpower is supplied to the controller 30 in response to the key switch 37being turned on. Accordingly, the controller 30 implements calculationsas will be described later, to control the rotation of the pulse motor32 by outputting the control signal to the pulse motor 32 and also tocontrol operations of a buzzer 39 and a warning lamp 40 by outputtingcontrol signals thereto.

Next, the construction of the traveling motor 1 will be explained. FIG.2 is a sectional view of the variable displacement traveling motor 1. Asshown in FIG. 2, a plurality of pistons 42 (only one of which is shownin the figure) are connected with a flange 41 of the output shaft 1 a ofthe traveling motor 1, along its circumferential direction. The pistons42 are slidably inserted into oil chambers 43 a formed in a cylinderblock 43 through piston rings 42 a. The end of the cylinder block 43comes into contact with a swash plate 44, and their contacting surfacesmutually define a circular cone shape. The swash plate 44 can be swungor inclined together with the cylinder block 43 in the direction of thearrow shown in the figure, and the motor displacement varies accordingto the swing amount or inclined angle of the swash plate.

An inlet or suction port and an outlet or delivery port of oil, notshown in the figure, are provided in the swash plate and a motor cover45 which is in contact with the swash plate 44, the suction port and thedelivery port extending over half a phase, respectively. And, thepressure oil from main pump 3 flows into the oil chambers 43 a throughthe suction port, while the oil from the oil chambers 43 a flows out tothe reservoir through the delivery port. Due to this, the pistons 42 areslid within the oil chambers 43 a, and, while the swash plate 44 is keptin contact with the cylinder block 43, the output shaft 1 a of the motor1 rotates as a unit with the cylinder block 43 and the pistons 42. Aninput shaft 7 a of the transmission 7 is connected by splines with themotor output shaft 1 a so that the rotation of the traveling motor 1 istransmitted to the transmission 7.

At this time, portions of the pressure oil which is supplied to the oilchambers 43 a from the main pump 3 leak into the drain chamber 11through gaps between the mutually contacting surfaces of the swash plate44 and the cylinder block 43, or gaps between the mutually slidingsurfaces of the pistons 42 and the oil chambers 43 a. This leakage oilreturns to the reservoir via a drain hole 11 a which is provided in thebottom of the motor casing 46.

The viscosity of the pressure oil decreases when the pressure oilsupplied to the traveling motor 1 becomes a high temperature due to, forinstance, the damage of hydraulic components and an oil cooler or thelike installed in the upper-structure. As a result, the oil film on thesliding surfaces of pistons 42 may be ruptured, which disturbs a smoothsliding operation of the pistons and may cause wear on such slidingsurfaces. The wear on the sliding surfaces may cause the followingproblems. In concrete term, the piston 42 is caused to stick in (tocontact directly with) the cylinder block 43, the cylinder block 43rotates while being dragged by the piston 42 and then, the gap betweenthe cylinder block 43 and the swash plate 44 becomes partiallyincreased. In other cases, the piston ring 42 a may be damaged, whichcauses the gap between the mutually sliding surfaces to become wider.Accordingly, a large amount of pressure oil from main pump 3 flows intothe drain chamber 11 through such gaps, and thereby the amount of oil inthe drain chamber 11 increases. As a result, the oil in the drainchamber 11 flows into the transmission 7 through seal rings SR. Due tothis, great resistance comes to act on the transmission 7 so that thetravelling performance of the vehicle deteriorates.

In this embodiment, in order to avoid the above mentioned problems, itis intended to detect the possible causes of the abnormal operation ofthe traveling motor 1 at the early stage using the temperature sensor35. That is, the sign of the abnormal operation is to be detected. Bydetecting the sign of the abnormal operation, a large amount of oilleakage from the hydraulic pump 1 to the drain chamber 11 may beprevented beforehand, and the damage upon the traveling motor 1 andmoreover negative consequences from this damage can be suppressed to theminimum.

FIG. 3 is a schematic illustration to explain details of the controller30. When the engine key switch (ignition key switch) 37 is turned on,the electric power is supplied to the controller 30 to start executionof its processing. A function generator 301 outputs a set signal to aset terminal S of a RS flip-flop 302 when the drain oil temperaturedetected by the temperature sensor 35 is greater than or equal to thepredetermined value Ta. It is to be noted that the predetermined valueTa represents a value of the drain oil temperature that lowers theviscosity of oil and is likely to cause the rupture of the oil film onthe sliding surfaces. When the detected temperature T reaches thepredetermined value Ta or higher, which shows the sign of the failure ofthe traveling motor 1, there is great possibility that a large amount ofdischarged oil from the pump flows into the drain chamber 11.

When the set signal is input to a set terminal S of the flip-flop 302,the flip-flop 302 outputs a high-level signal from its terminal Q tochange over a switchover circuit 303 to its contact “a” side. As aresult, electrical power is supplied to a buzzer 39 and a warning lamp40, so that the buzzer emits sound and the buzzer lamp 40 isilluminated.

When a reset switch 36 is turned on, the reset switch 36 outputs a resetsignal to a reset terminal R of the flip-flop 302. The flip-flop 302sets low-level in the terminal Q in response to this reset signal, andthe switchover circuit 303 is then switched to its contact “b” side. Asa result, the supply of electrical power to the buzzer 39 and thewarning lamp 40 is interrupted so that the buzzer sound is brought to ahalt and the warning lamp 40 is extinguished.

A function by which the engine speed should increase along with increaseof the traveling pilot pressure is set in advance in the functiongenerator 304, as schematically shown in the figure. The functiongenerator 304 sets the rotational speed N corresponding to the detectedvalue P1 from the pressure sensor 34 based upon this function, andoutputs this set value N to a switchover circuit 305. The switchovercircuit 305 is changed over according to the changeover direction of theswitchover circuit 303. In other words, the switchover circuit 305 isswitched to its contact “a” side when the switchover circuit 303 isswitched to its contact “a” side, while the switchover circuit 305 isswitched to its contact “b” side when the switchover circuit 303 isswitched to its contact “b” side. Accordingly, the switchover circuit305 selects either the rotational speed N as set by the functiongenerator 304 or an idling rotational speed Ni which is set in advancein a rotational speed setting device 306, and outputs its selectedrotational speed to a servo control section 307 as a target rotationalspeed Ny. In the servo control section 307, the target rotational speedNy is compared with the control rotational speed Nθ which corresponds tothe amount of displacement of the governor lever as detected by thepotentiometer 33, and the pulse motor 32 is controlled so as to bringthe control rotational speed Nθ to match the target rotational speed Ny,according to the procedure shown in FIG. 4.

Referring to FIG.4, first in step S21, the rotational speed commandvalue Ny and the control rotational speed Nθ are read in, and then theflow of control proceeds to step S22. In step S22, Ny is subtracted fromNθ, (Nθ−Ny), and the result of this subtraction, i.e. the rotationalspeed differential A, is stored in a memory. In step S23, it makes adecision as to whether or not |A|≧K, by using a standard rotationalspeed differential K provided beforehand. If an affirmative decision ismade, the flow of control proceeds to step S24 in which a decision ismade as to whether or not the rotational speed differential A>0. If A>0,it implies that the control rotational speed Nθ is greater than therotational speed command value Ny, in other words, the controlrotational speed is higher than the target rotational speed, the flow ofcontrol then proceeds to step S25 in which a signal for instructingreverse rotation of the motor is output to the pulse motor 32 in orderto reduce the engine speed. As a result, the pulse motor 32 is caused torotate in reverse so that the rotational speed of the engine 2 drops.

On the other hand, if A≦0, it implies that the control rotational speedNθ is lower than the rotational speed command value Ny, that is, thecontrol rotational speed is lower than the target rotational value, asignal for instructing normal rotation of the motor is output in orderto increase the engine speed, in step S26. As a result, the pulse motor32 performs normal rotation to increase the engine speed. If a negativedecision is made in step S23, the flow of control proceeds to step S27to output a motor stop signal. Therefore, the rotational speed of theengine 2 is maintained constant. After the appropriate one of the stepsS25 to S27 has been executed, the flow of control returns to thebeginning of this flow chart.

The outstanding features of the operation of this failure detectiondevice for a hydraulic drive vehicle constructed as described above willnow be explained in concrete term.

(1) During normal operation of the traveling motor

While the traveling motor 1 operates normally, the piston 42 slidessmoothly and the drain oil temperature remains lower than or equal tothe predetermined value Ta. Accordingly, the switchover circuit 303 andthe switchover circuit 305 of the controller 30 are switched to theircontacts “b” side, respectively, so that the buzzer 39 and the warninglamp 40 is turned off. In this condition, if the forward/backwardswitchover valve 25 is switched to forward traveling or to reversetraveling, and also the accelerator pedal 22 is stepped upon, thetraveling pilot pressure P1 is generated in correspondence to the amountby which the accelerator pedal is operated. The servo control section307 compares the target rotational speed Ny according to this travelingpilot pressure P1 with the control rotational speed Nθ corresponding tothe detected value from the potentiometer 33, and then controls thepulse motor 32 to bring both rotational speeds to agree with each other.Therefore, the engine speed increases in line with the increase of theamount of pedal operation.

(2) When operation of the traveling motor becomes abnormal

When the temperature of the pressure oil supplied to the traveling motor1 becomes higher, there is a possibility that the oil film on thesliding surfaces of the motor pistons may be ruptured and causes thewear upon the sliding surfaces. When the drain oil temperature rises tothe predetermined value Ta, the function generator 301 outputs the setsignal to the set terminal of the flip-flop 302. The flip-flop 302 thenoutputs a high-level signal from its terminal Q to change over aswitchover circuit 303 to its contact “a” side. Due to this, the buzzersound is emitted and also the warning lamp 40 is illuminated.Accordingly, the operator recognizes the sign of the failure of thetraveling motor 1, and is able to perform an appropriate operation, e.g.a brake operation, to stop the rotation of the traveling motor 1 inresponse to an abnormal state of the motor 1. As a result, it ispossible to prevent the damage on the traveling motor 1 from happeningand moreover to suppress negative consequences from the damage of themotor 1, for instance a copious oil flow into the drain chamber 11, tothe minimum.

The switchover circuit 305 is also changed over to the contact “a” sidein response to the switchover circuit 303 being changed over. Due tothis, the engine speed is lowered to its idling rotational speed Niregardless of the pedal actuation amount, and the rotational speed ofthe traveling motor 1 also drops in line with reduction in amount of thedelivery oil from the pump. As a result, the traveling motor 1 isautomatically prevented from the wear. Since the vehicle is decelerated,the vehicle can be promptly stopped when the brake is operated.Moreover, useless consumption of fuel can be prevented.

The traveling motor 1 can be restarted when the reset switch 36 isoperated. In the state in which the drain oil temperature is below thepredetermined value Ta, when the reset switch 36 is operated, theterminal Q of the flip-flop 302 is set to low level to switch theswitchover circuit 303 to the contact “b” side and then the switchovercircuit 305 is switched to the contact “b” side. Due to this, the buzzersound is stopped and also the warning lamp 40 is extinguished. In otherwords, the operator is able to stop warning devices from operating athis will. Moreover, it becomes again possible to control the enginespeed in accordance with operation of the accelerator pedal. As aresult, when the vehicle is to be transported upon a trailer for therepair of the traveling motor 1, it is possible to load the vehicle ontothe trailer by driving it under its own power. It should be understoodthat, instead of operating the reset switch 36, it would also beacceptable to turn off the engine key switch 37.

According to the first embodiment as described above, when the sign ofthe breakdown of the traveling motor 1 is detected based upon the risein temperature of the drain oil, the warning, such as buzzer sounds andillumination of the warning lamp 40 is issued. Therefore, the operatoris able to perform appropriate operation to stop the motor 1 beforedamaging the traveling motor 1 and thus it is possible to prevent thedamage on the traveling motor 1 from happening. Moreover, the enginespeed is lowered to the idling rotation speed Ni to restrict the driveof the traveling motor 1 when it shows the sign of a breakdown of themotor, which makes possible to automatically prevent the traveling motor1 from being damaged. Since the engine speed is lowered to the idlingrotational speed and the vehicle is slowed down, it is possible to pullthe vehicle slowly to the shoulder of the road and to stop. Moreover, auseless waste of fuel can be prevented. In addition, the warning is keptissued and restriction upon the traveling of the vehicle is maintaineduntil the reset switch 36 is operated or alternatively the engine keyswitch 37 is turned off. Therefore, an operator is able to recognize theabnormal state of the traveling motor 1. In the state in which the drainoil temperature is below the predetermined value Ta, if the reset switch36 is operated or the engine key switch 36 is turned on alternatively,the engine speed can again be increased according to the operation ofthe accelerator pedal and it is possible to load the vehicle upon thetrailer or the like easily.

Second Embodiment

When the traveling motor 1 over-rotates or rotates at extremely highspeed, friction on the sliding surfaces of the pistons 42 increases,which may cause the wear on the pistons 42, and the traveling motor 1may be damaged. Thus, in the second embodiment, it is determined thatthe sign of the failure of the traveling motor 1 is detected when therotational speed of the traveling motor 1 increases to predeterminedvalue Na or higher. The second embodiment of the present invention willnow be explained with reference to FIGS. 5 and 6. FIG. 5 is a circuitdiagram showing the structure of a wheeled hydraulic excavator which isequipped with a failure detection device according to the secondembodiment, and FIG. 6 schematically illustrates details of a controller30A according to the second embodiment. It should be noted that the samereference numerals are used for elements similar to that of FIGS. 1 and3, and the explanations will focus on the points different therefrom.

As shown in FIG. 5, a rotational speed sensor 26 that detects a motorrotational speed is provided at the output shaft 1 a of the motor. Therotational speed sensor 26 is connected with the controller 30A insteadof the temperature sensor 35. As shown in FIG. 6, a function generator301 outputs a set signal to a set terminal S of a RS flip-flop 302 whenthe motor rotational speed detected by the rotational speed sensor 26 ishigher than or equal to the predetermined value Na. It in to beunderstood that the predetermined value Na represents a value of therotational speed at which the wear may be caused upon the pistons 42.Accordingly, the switchover circuits 303 and 305 are switched to theircontacts “a” side, and thereby the warning devices are operated. Inaddition, the engine speed is limited to the idling rotational speed Ni.

In the second embodiment as described above, the sign of the failure ofthe motor 1 is detected based upon the over-rotation of the travelingmotor 1. Therefore, it is possible to predict failure of the travelingmotor 1 before the drain oil temperature actually rises and to stop thetraveling motor 1 at earlier stage.

Third Embodiment

In the third embodiment, it is determined that the sign of the failureof the traveling motor 1 is detected when cavitation has been generated.The third embodiment of the present invention will now be explained withreference to FIGS. 7 and 8. FIG. 7 is a circuit diagram showing theconstruction of a wheeled hydraulic excavator which is equipped with afailure detection device according to the third embodiment, and FIG. 8schematically illustrates the structure of a controller 30B according tothe third embodiment. It should be noted that the same referencenumerals are used for elements similar to that of FIGS. 1 and 3, and theexplanations will focus on the points different therefrom.

As shown in FIG. 7, pressure sensors 27-29 are provided at the inletport, the outlet port and the make-up port of the traveling motor 1,respectively. These pressure sensors 27-29 each detects motor inletpressure during normal rotation, reverse rotation and braking operation.As shown in FIG. 8, function generators 322-324 output a high-levelsignal to a OR gate 325 when the pressure detected by theircorresponding pressure sensors 27-29 is negative pressure (equal to 0 orless). When at least one of the detected values of the pressure sensors27-29 is negative, that is, cavitation has occurred, the OR gate 325outputs a set signal to a set terminal S of a flip-flop 302.Accordingly, the switchover circuits 303 and 305 are changed to theircontact “a” side, and thereby the warning devices are operated and theengine speed is restricted to the idling rotational speed Ni.

According to the third embodiment as described above, since the sign ofthe breakdown of the motor 1 is detected when the cavitation hasoccurred, it is possible to stop the cavitation promptly so thatproblems caused along with generation of the cavitation, such as noiseor the like, can be avoided.

Fourth Embodiment

While, in the first embodiment, the engine speed is lowered to theidling rotational speed Ni to restrict the vehicle speed when the signof the failure of the traveling motor 1 is detected, the vehicle will bestopped in the fourth embodiment. The fourth embodiment of the presentinvention will now be explained with reference to FIGS. 9 and 10. FIG. 9is a circuit diagram showing the structure of a wheeled hydraulicexcavator equipped with a failure detection device according to thefourth embodiment, and FIG. 10 schematically illustrates details of acontroller 30C according to the fourth embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanations will focus on the pointsdifferent therefrom.

As shown in FIG. 9, the line between the traveling pilot valve 23 andthe slow-return valve 24 can be connected with the reservoir through asolenoid valve 47. The solenoid valve 47 is controlled by a controlsignal from the controller 30C. A solenoid 47 a of the solenoid valve 47is connected with the switchover circuit 303 as shown in FIG. 10.

When the drain oil temperature rises to the predetermined value Ta andthe switchover circuit 303 is switched to the contact “a” side, thesolenoid 47 a is excited to switch the solenoid valve 47 to its positionB. As a result, the pressure oil having acted on the pilot port ofcontrol valve 4 returns to the reservoir via the forward/backwardswitchover valve 25, the slow-return valve 24 and the solenoid valve 47,and the control valve 4 is driven back to its neutral position. Thesupply of pressure oil to the traveling motor 1 is thus intercepted, andeven if the accelerator pedal 22 is actuated the vehicle is preventedfrom traveling. In addition, the warning devices start operating, andthe engine speed is limited to the idling rotational speed Ni.

While the solenoid 47 a is excited, if the reset switch 36 is actuated,the switchover circuit 303 is switched to the contact “b” side.Accordingly, the solenoid 47 a is demagnetized, and the solenoid valve47 is switched to its position A. As a result, the traveling pilotpressure corresponding to the operation of the accelerator pedal is madeto act on the pilot port of the control valve 4, and the supply of thepressure oil to the traveling motor 1 becomes possible.

According to the fourth embodiment as described above, when the sign ofthe failure in the traveling motor 1 is shown, the traveling pilotpressure is made to return to the reservoir by the operation of thesolenoid valve 47. As a result, even if the brake is not operated thevehicle stops promptly, and it is possible to suppress damage of thetraveling motor 1 and any negative influences which may be caused bythis damage to the minimum.

Fifth Embodiment

While, in the fourth embodiment described above, the vehicle is stoppedwhen the sign of the failure of the traveling motor 1 is detected, thebrake (a parking brake) is additionally applied in the fifth embodiment.The fifth embodiment of the present invention will now be explained withreference to FIGS. 11 and 12. FIG. 11 is a circuit diagram showing thestructure of a wheeled hydraulic excavator which is equipped with afailure detection device according to the fifth embodiment, and FIG. 12schematically illustrates details of a controller 30D according to thefifth embodiment. It should be noted that the same reference numeralsare used for elements similar to that of FIGS. 9 and 10, and theexplanation will focus on the points different therefrom.

In FIG. 11, a speed sensor 48 that detects the velocity of the vehicleand a solenoid valve 49 for operating the parking brake are additionallyprovided to the circuit shown in FIG. 9. It should be noted that theparking brake is of a type that is well-known and is operated accordingto the operation of the solenoid valve 49, and the drawing of which isomitted herein. As shown in FIG.12, a solenoid 49 a of the solenoidvalve 49 is connected with the switchover circuit 303 via the switchovercircuit 308. A function generator 309 switches over the switchovercircuit 308 according to a detection value V of the speed sensor 48.

While the vehicle is traveling, the function generator 309 switches theswitchover circuit 308 to its contact “b” side as shown in the figure.Accordingly, the solenoid 49 a is demagnetized so that the parking brakeis released. When the sign of the breakdown of the traveling motor 1 isdetected and then the switchover circuit 303 is switched to the contact“a” side, the solenoid 47 a of the solenoid valve 47 is excited so thatthe vehicle stops, as described above. And, the function generator 309switches the switchover circuit 308 to its contact “a” side when it isdetected that the vehicle has stopped, in other words the vehicle speedbecomes zero. As a result, the solenoid 49 a is excited to operate theparking brake. When the switchover circuit 303 is switched to thecontact “b” side in response to the operation of the reset switch 36,the solenoid 49 a is demagnetized so that the parking brake iscancelled. It is also possible to provide a timer connected to thefunction generator 309 so as to switch the switchover circuit 308 to thecontact “a” side when a predetermined time period is detected after thevehicle speed becomes zero.

According to the fifth embodiment as described above, when the vehicleis caused to stop according to the sign of the failure of the travelingmotor 1, the parking brake is engaged to operate. Therefore, it ispossible to maintain the stationary state of the vehicle even when it ison the slope or the like.

Sixth Embodiment

While, in the fourth embodiment, the engine is caused to stop when thesign of the failure of the traveling motor 1 is shown, in addition tothis function, the engine 2 is prohibited from restarting in the sixthembodiment. The sixth embodiment of the present invention will now beexplained with reference to FIGS. 13 and 14. FIG. 13 is a circuitdiagram showing the construction of a wheeled hydraulic excavator whichis equipped with a failure detection device according to the sixthembodiment, and FIG. 14 schematically illustrates the structure of acontroller 30E according to the sixth embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 9 and 10, and the explanation will focus on the pointsdifferent therefrom.

As shown in FIG.13, a starting motor 51 is connected with the controller30E, and the drive of the starting motor 51 is controlled thereby. Asshown in FIG. 14, the engine key switch 37 is connected with thestarting motor 51 via a relay 310, and the output terminal of thechangeover switch 303 is connected with a coil of the relay 310.Accordingly, when the sign of the breakdown of the traveling motor 1 isdetected and the switchover circuit 303 is switched to the contact “a”side, the solenoid 47 a is excited to stop the vehicle. In addition, thecoil of the relay 310 is supplied with actuating electrical energy sothat the relay contact is switched to its contact “R1” side. As aresult, the supply of electricity to the starting motor 51 is cut, andit is impossible to start the engine 2 even if the engine key switch 37is turned on. It should be noted that the parking brake may also beoperated when the vehicle has stopped.

In such a state, if the reset switch 36 is actuated, the switchovercircuit 303 is switched to the contact “b” side, and the supply ofelectricity to the coil of the relay 310 is intercepted. The relaycontact is thus switched to the contact “R2” side, which makes possibleto restart the engine. It should be noted that it would also be possibleto restart the engine 2, as an alternative to operation of the resetswitch 36, by a repairman, etc. using some apparatuses to supply anexternal signal of some type. In this manner, it would not be possiblefor an operator to restart the engine upon his own decision.

According to the sixth embodiment, when the sign of the failure of thetraveling motor 1 is detected, the engine 2 can not be restarted.Therefore, an operator will not imprudently restart the engine 2 todrive the vehicle, and it is possible to suppress negative consequencesfrom the damage of the traveling motor 1 to the minimum.

Seventh Embodiment

While, in the first embodiment, the engine speed is limited to theidling rotational speed Ni when the sign of the failure of the travelingmotor 1 is detected regardless of the traveling state or the workingstate, the engine speed will be limited only during the traveling statein the seventh embodiment. The seventh embodiment of the presentinvention will now be explained with reference to FIGS. 15 and 16. FIG.15 is a circuit diagram showing the structure of a wheeled hydraulicexcavator equipped with a failure detection device according to theseventh embodiment, and FIG. 16 schematically illustrates details of acontroller 30F according to the seventh embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanations will focus on the pointsdifferent therefrom.

As shown in FIG. 15, a forward/reverse changing switch 52 for outputtinga switching command to the forward/reverse switchover valve 25, and abrake switch 53 for outputting an operate command to a work brake notshown in the figures are also connected to the controller 30F. As shownin FIG. 16, a switchover circuit 311 is connected with the terminal Q ofthe flip-flop 302, and the switchover circuit 311 is switched accordingto a signal from a work detection section 312. The signals from theforward/reverse changing switch 52 and the brake switch 53 are input tothe work detection section 312. The work detection section 312 sets theswitchover circuit 311 to the contact “a” side when the forward/reverseswitchover valve 25 is in the neutral position and also the work brakeis being operated, while in other conditions, the switchover circuit 311is switched to the contact “b” side.

In this manner, the switchover circuit 311 is switched to the contact“b” while the vehicle is traveling, and if the sign of the failure ofthe traveling motor 1 is shown, then the switchover circuits 303 and 305are switched to the contact “a” side to restrict the engine speed to theidling rotational speed Ni. In such a condition, if the forward/reverseswitchover valve 25 is set to the neutral position in response to theoperation of the forward/reverse changing switch 52, and also the workbrake is operated by the operation of the brake switch 53, theswitchover circuit 311 is then switched to the contact “a” side. Inresponse to this switchover, the switchover circuits 303 and 305 areboth switched to the contact “b” side to cancel the restriction upon theengine speed. As a result, the engine speed can be increased accordingto the pedal actuation, and it is possible to work as usual. In thiscondition, if the forward/reverse switchover valve 25 is switched to theforward traveling or the reverse traveling in order to cause the vehicleto travel, the switchover circuits 303 and 305 are both switched to thecontact “a” side. As a result, the engine speed is again made todecrease to the idling rotational speed Ni.

According to the seventh embodiment as described above, it is detectedas to whether or not the vehicle has started the work operationaccording to actuations of the forward/reverse changing switch 52 andthe brake switch 53. It is possible to continue working in the normalmanner even when the traveling motor 1 has broken down since therestriction of the engine speed is released during working. It should benoted that the seventh embodiment can be applied, not only to a systemwhich restricts the engine speed but also, in the same manner, tosystems which controls the vehicle travel in other ways, such as bystopping the vehicle traveling, by preventing the engine fromrestarting, or by engaging the parking brake to operate.

It should be noted, while in the first to seventh embodiments the enginespeed is limited to the idling rotational speed Ni when the sign of thefailure of the traveling motor 1 is detected, it is also possible,instead of restricting to the idling rotational speed Ni, to set arotational speed corresponding to the traveling pilot pressure. In thiscase, the switchover circuit 305 would become unnecessary. Moreover,while, in the fourth to seventh embodiments, the sign of the travelingmotor 1 is detected according to increase in the drain oil temperature,it is also possible to detect the sign of the traveling motor 1 basedupon the motor rotational speed or the occurrence of the cavitaion inthe same manner as the second or third embodiment.

Moreover, although in the first to seventh embodiments, the buzzer soundis emitted along with the illumination of the warning lamp 40 when signof the failure of the traveling motor 1 is detected, it would also beacceptable to provide one of the warning devices. Furthermore, it wouldbe possible to flash the hazard warning lamps which are provided aroundthe vehicle, in order to arouse the attention around the vehicle.Although, upon detection of the sign of the failure of the travelingmotor 1, the provision of warning and the restriction of the vehicletraveling have been performed at the same time, it would be alsoacceptable to perform only one of them. Moreover, although the drivingof the traveling motor 1 is limited, driving of actuators other than thetraveling motor 1, such as a swing motor, may as well be restricted. Inaddition, signs of failure of the actuators other than the travelingmotor may also be detected.

INDUSTRIAL APPLICABILITY

While a failure detection device for a hydraulic motor has beenexplained in terms of application to a wheeled hydraulic excavator byway of example, it would also be possible, in the same manner, to applythe failure detection device of the hydraulic motor according to thepresent invention to a crawler hydraulic excavator, or to other kinds ofhydraulic drive vehicles.

1. A failure detection device for a hydraulic motor, comprising: ahydraulic pump that is driven by a prime mover; a hydraulic motor thatis driven by hydraulic oil discharged from the hydraulic pump; anabnormality sign detection device that detects a sign indicating that anabnormal operation will occur in the hydraulic motor; and a driverestriction device that restricts a driving of the hydraulic motor whenthe sign of the abnormal operation of the hydraulic motor is detected bythe abnormality sign detection device.
 2. A failure detection device fora hydraulic motor according to claim 1, wherein: the drive restrictionswitch is reset by actuation of an ignition key switch.
 3. A failuredetection device for a hydraulic motor according to claim 1, wherein:the hydraulic motor is a hydraulic motor for traveling.
 4. A failuredetection device for a hydraulic motor according to claim 3, wherein:the drive restriction device is a rotational speed restriction devicethat restricts a rotational speed of the prime mover, and the rotationalspeed restriction device lowers the rotational speed of the prime moverto a predetermined rotational speed when the sign of the abnormaloperation of the hydraulic motor for traveling is detected by theabnormality sign detection device.
 5. A failure detection device for ahydraulic motor according to claim 3, wherein: the drive restrictiondevice is a traveling prevention device that prevents the driving of thehydraulic motor for traveling, and the traveling prevention deviceprevents the hydraulic motor for traveling from being driven when thesign of the abnormal operation of the hydraulic motor for traveling isdetected by the abnormality sign detection device.
 6. A failuredetection device for a hydraulic motor according to claim 3, furthercomprising: a stopping detection device that detects whether thehydraulic motor for traveling has stopped; and a brake device thatapplies a brake upon the hydraulic motor for traveling when theabnormality sign detection device detects the sign of the abnormaloperation of the hydraulic motor for traveling and moreover the stoppingdevice detects that the hydraulic motor for traveling has stopped.
 7. Afailure detection device for a hydraulic motor according to claim 3,further comprising: a restart prevention device that prevents arestarting of the prime mover when the sign of the abnormal operation ofthe hydraulic motor for traveling is detected by the abnormality signdetection device.
 8. A failure detection device for a hydraulic motoraccording to claim 1, further comprising: a warning device that issues awarning when the sign of the abnormal operation of the hydraulic motoris detected by the abnormality sign detection device.
 9. A failuredetection device for a hydraulic motor according to claim 1, furthercomprising: a reset command switch that resets the drive restrictiondevice.
 10. A failure detection device for a hydraulic motor accordingto claim 1, further comprising: a working detection device that detectsa working state; and a drive restriction control device that disables adrive restriction on the hydraulic motor by the drive restriction devicewhen the working detection device detects the working state.
 11. Afailure detection device for a hydraulic motor according to claim 1,wherein: the abnormality sign detection device detects the sign of theabnormal operation of the hydraulic motor based upon an inlet pressureof the hydraulic motor.
 12. A failure detection device for a hydraulicmotor according to claim 1, wherein: the abnormality sign detectiondevice detects the sign of the abnormal operation of the hydraulic motorbased upon a temperature of drain oil from the hydraulic motor.
 13. Afailure detection device for a hydraulic motor according to claim 1,wherein: the abnormality sign detection device detects the sign of theabnormal operation of the hydraulic motor based upon a rotational speedof the hydraulic motor.
 14. A failure detection device for a hydraulicmotor, comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor that is driven by hydraulic oil discharged from thehydraulic pump; an abnormality sign detection device that detects a signindicating that an abnormal operation will occur in the hydraulic motor;and a warning device that issues a warning when the sign of the abnormaloperation of the hydraulic motor is detected by the abnormality signdetection device.
 15. A failure detection device for a hydraulic motoraccording to claim 14, further comprising: a working detection devicethat detects a working state, and a warning control device that disablesthe warning device from issuing the warning when the working detectiondevice detects the working state.
 16. A failure detection device for ahydraulic motor according to claim 14, wherein: the abnormality signdetection device detects the sign of the abnormal operation of thehydraulic motor based upon a temperature of drain oil from the hydraulicmotor.
 17. A failure detection device for a hydraulic motor according toclaim 14, further comprising: a reset command switch that resets thewarning device.
 18. A failure detection device for a hydraulic motoraccording to claim 14, wherein: the abnormality sign detection devicedetects the sign of the abnormal operation of the hydraulic motor basedupon a rotational speed of the hydraulic motor.
 19. A failure detectiondevice for a hydraulic motor according to claim 2, wherein: the warningdevice is reset by actuation of an ignition key switch.
 20. A failuredetection device for a hydraulic motor according to claim 14, wherein:the abnormality sign detection device detects the sign of the abnormaloperation of the hydraulic motor based upon an inlet pressure of thehydraulic motor.
 21. A hydraulic drive vehicle, comprising: a hydraulicpump that is driven by a prime mover; a hydraulic motor for travelingthat is driven by hydraulic oil discharged from the hydraulic pump; anabnormality sign detection device that detects a sign indicating that anabnormal operation will occur in the hydraulic motor for traveling; anda warning device that issues a warning when the sign of the abnormaloperation of the hydraulic motor for traveling is detected by theabnormality sign detection device.
 22. A hydraulic drive vehicle,comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedby the hydraulic pump; an abnormality sign detection device that detectsa sign indicating that an abnormal operation will occur in the hydraulicmotor for traveling; and a drive restriction device that restricts adriving of the hydraulic motor for traveling when the sign of theabnormal operation of the hydraulic motor for traveling is detected bythe abnormality sign detection device.